(1) Field of the Invention
This invention relates to imaging apparatus for use in nuclear medicine, and more particularly to an improvement in scintillation cameras used in static radiography with a fixed detector and in SPECT (Single Photon Emission Computerized Tomography) with a revolving detector.
(2) Description of the Related Art
A nuclear medicine imaging apparatus detects, outside the body examined, the radiation released by radioactive substances introduced into the body. Prior to release of the radiation outside the body, Compton scatter and absorption take place owing to body tissues. It is necessary to effect a correction to these phenomena. Conventional techniques of such correction are disclosed in U.S. Pat. No. 4,780,823 and Japanese Patent Publication (Unexamined) No. 62-167491, for example.
However, these conventional techniques have the disadvantages of being unsatisfactory in quantification and involving enormous amounts of computation processing. In U.S. Pat. No. 4,780,823, a fixed energy weight function is approximated regardless of locations in order to correct scatter in real time. This results in poor quantification. In Japanese Patent Publication (Unexamined) No. 62-167491, scatter correcting coefficients and energy weight functions are varied for individual locations (pixels) based on energy spectral information. Although quantification is good, this technique is not practical in that a matrix on the order of 64.times.64 as in SPECT is its limit, and that statistical errors would occur and enormous amounts of computation processing would be involved for a matrix of 512.times.512 as in static radiography.
Furthermore, while only data of small counts are available from ordinary clinical procedures, the conventional techniques put the obtained raw data per se to correction processing. As a consequence, considerable statistical errors tend to occur, which in turn produce even greater computational errors. Resultant images have a great deal of noise in background regions and cold spots.